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• Boost Thread Specific Storage Question (boost/thread/tss.hpp)

  - by Hassan Syed

  The boost threading library has an abstraction for thread specific (local) storage. I have skimmed over the source code and it seems that the TSS functionality can be used in an application with any existing thread regardless of weather it was created from boost::thread --i.e., this implies that certain callbacks are registered with the kernel to hook in a callback function that may call the destructor of any TSS objects when the thread or process is going out of scope. I have found these callbacks. I need to cache HMAC_CTX's from OpenSSL inside the worker threads of various web-servers (see this, detailed, question for what I am trying to do), and as such I do not controll the life-time of the thread -- the web-server does. Therefore I will use the TSS functionality on threads not created by boost::thread. I just wanted to validate my assumptions before I started implementing the caching logic, are there any flaws in my logic ?

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• mysql, sqlite database source code

  - by Yang

  hi guys, i know implementing database is a huge topic, but i want to have a basic understanding of how database systems works (e.g. memory management, binary tree, transaction, sql parsing, multi-threading, partitions, etc) by investigating the source code of the database, since there are a few already proven very robust open source databases like mysql, sqlite and so on. however, the code are very complicated and i have no clue where to start. also i find that the old school database textbooks are only explaining the theory, not the implementation details. Can anyone suggest how should i get started and is there any books that emphasis on the technology and techniques of building dbms used in modern database industry? Thank in advance!

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• How to deal with OpenMP thread pool contention

  - by dpe82

  I'm working on an application that uses both coarse and fine grained multi-threading. That is, we manage scheduling of large work units on a pool of threads manually, and then within those work units certain functions utilize OpenMP for finer grain multithreading. We have realized gains by selectively using OpenMP in our costliest loops, but are concerned about creating contention for the OpenMP worker pool as we add OpenMP blocks to cheaper loops. Is there a way to signal to OpenMP that a block of code should use the pool if it is available, and if not it should process the loop serially?

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• Qt undocumented method setSharable

  - by soxs060389

  I stumbled about a method which seems to be present in all DataObjects like QList, QQueue, QHash... I even investigated so far i can see the source code of it, which is inline void setSharable(bool sharable) { if (!sharable) detach(); d->sharable = sharable; } in qlist.h (lines 117) but what effect does it have on the QList, QQueue, QHash... ? And is it in any way related to threading? (which sounds reasonable) Thanks for any answer, and please only answer if you got actual knowledge.

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• Simple, non-blocking way to sleep?

  - by OverTheRainbow

  Hello I googled for this and read some threads here, but I haven't found a simple way to have a VB.Net application sleep for a little while and still keep the application responsive: Imports System.Net Imports System.IO Imports System.Text Imports System.Text.RegularExpressions Imports System.Threading.Thread [...] 'How to keep screen frop freezing? While True ListBox1.Items.Clear() ListBox1.Items.Add("blah") 'Not much difference ListBox1.Refresh() 'Wait 1mn Sleep(60000) End While Is there really no simple, non-blocking solution to have a VB.Net application wait for a few seconds? Thank you.

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• OpenMP timer doesn't work on inline assembly code?

  - by Brett

  I'm trying to compare some code samples for speed, and I decided to use the OpenMP timer since I'll eventually be multi threading the code. The timer works great on two of my four code snippets, but not on the other two start=omp_get_wtime(); /*code here*/ finish = omp_get_wtime() - start_time; The four code here sections are serial code, xmmintrin.h code, and two inline assembly codes. The serial and xmminstrin.h code are able to be timed, but the inline assembly codes returns -1.#IND00 for a time. I can't seem to figure out why this is? Thanks for any help or suggestions!

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• Javascript - why do I sometimes fail to read file content with GDownloadUrl?

  - by Daj pan spokój

  Hi everybody. I try to read some file with google's GDownloadUrl and it works only from time to time. failure means fileRows == "blah blah" success means fileRows == (real file content) I've noticed, however, that when I cease (with Firebug) the execution on line 3 for a couple of seconds, it succeeds more often. Maybe it is some kind of threading bug, then? Do You guys have any tip or idea? 1 var fileContent = "blah blah"; 2 availabilityFile = "input/available/" + date + ".csv"; 3 GDownloadUrl(availabilityFile, function(fileData) { 4 fileContent = fileData; 5 }); 6 fileRows = fileContent.split("\n");

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• A question about some code from TBB book, Thanks.

  - by Jackie

  I am reading the book: Intel Threading Building Blocks. I often have difficulties understanding them. For example,the following code is from the book(page 112): Node* AllocateNode() { Node* n; FreeListMutexType::scoped_lock lock; lock.acquire(FreeListMutex); n=FreeList; if(n) Freelist=n->next; lock.release(); if(!n) n=new Node(); return n; } There is other introduction regarding this code. I can not understand it. What does it means? How can I understand this book better? Thanks.

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• Python thread pool similar to the multiprocessing Pool?

  - by Martin

  Is there a Pool class for worker threads, similar to the multiprocessing module's Pool class? I like for example the easy way to parallelize a map function def long_running_func(p): c_func_no_gil(p) p = multiprocessing.Pool(4) xs = p.map(long_running_func, range(100)) however I would like to do it without the overhead of creating new processes. I know about the GIL. However, in my usecase, the function will be an IO-bound C function for which the python wrapper will release the GIL before the actual function call. Do I have to write my own threading pool?

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• Restart IIS7 webapp for debug in VS2008

  - by spender

  I'm developing an ASP.NET asyc generic handler which uses a static System.Threading.Timer instance to feed data to the response output stream while the context is in the asynchronous phase. I'm having issues at startup that I'd like to debug. Currently, because of the long-lived nature of the timer, I'm manually killing w3wp.exe in order to cause the application to restart. I'm aware that there are other ways to do this, but this is the best workflow I can find! Isn't there a way to force a cold start when I hit f5, instead of the standard VS approach of attaching to the existing IIS process?

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• Import xml to database with high end performance and Audit log- A best Practice

  - by karthik

  Hi, I have to import big xml files to Ms SQL 2005 Database by using C# with high end Performance. Even if any record fails in middle, i have to take next record for process and failed record need to log for audit. I don't want to put insert query with in for loop. Could you please suggest a best way to do this. If I can use bulkcopy methods or Data Adapter update methods- Its very nice, But if any record fails, execution of that statement breaks and rolled back totally, right? Any alternatives and Best practices with example please..? Is Multi-threading works for me to improve performance..? Give me example please. Thanks Karthikeyan

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• How to cause AggregateException with TPL?

  - by Sly

  I'm trying to recreate the conditions that will cause this exception: System.AggregateException: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread.` I wrote this program thinking I'd cause the exception but it does not: using System; using System.Threading.Tasks; namespace SomeAsyncStuff { class Program { static void Main(string[] args) { Task.Factory.StartNew(() => { throw new NullReferenceException("ex"); }); GC.Collect(); Console.WriteLine("completed"); } } } In my real application, I use TPL and I did not code my exception handling right. As a result I get that exception. Now I'm trying to recreate the same conditions in a separate program to experiment with unobserved exceptions.

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• My HttpHandler doesn't want to create directory on a network

  - by Daok

  I use this simple line of code inside my HttpHandler: Directory.CreateDirectory(@"\\srv-001\dev\folderToCreate\"); I receive an UnauthoridezAccessException telling me that the access to the path is denied. From here, I create a little Dos application in C# doing the same thing and I was able to create the folder. So, I thought that it might be that IIS is running on a different user than myself. I went to IIS and changed the Application pool to a Custom user, myself. But, unfortunately, I got the same exception. I have try to create a Share folder on my computer and I can create directory. Also, when debugging I can see that System.Threading.Thread.CurrentPrincipal.Identity have its AuthenticationType to "", IsAuthenticated to false and name to "". So, with all those tests I can conclude that the HttpHandler that receive the file cannot create a directory because of some security access. How can I grand access to my HttpHandler to be able to create a directory (and files) to a network folder?

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• System.WIndows.Application static members are thread safe?

  - by Lirik

  The Application static members are supposed to be thread safe: The public static (Shared in Visual Basic) members of this type are thread safe. In addition, the FindResource and TryFindResource methods and the Properties and Resources properties are thread safe.1 How much can we trust that statement in a multithreaded environment when calling static member methods of System.Windows.Application? Update: It's all in reference to this question: http://stackoverflow.com/questions/2463822/threading-errors-with-application-loadcomponent-key-already-exists/2463866#2463866 I never thought I'd see a real bug in the library, but this must be the day for me... that question seems to show a genuine bug. Usually it's "user error," but this doesn't seem to be the case.

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• How to re-use a thread in Java ?

  - by David

  I am a building a console Sudoku Solver where the main objective is raw speed. I now have a ManagerThread that starts WorkerThreads to compute the neibhbors of each cell. So one WorkerThread is started for each cell right now. How can I re-use an existing thread that has completed its work? The Thread Pool Pattern seems to be the solution, but I don't understand what to do to prevent the thread from dying once its job has been completed. ps : I do not expect to gain much performance for this particular task, just want to experiment how multi-threading works before applying it to the more complex parts of the code. Thanks

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• Python GUI Scraper hanging issues.

  - by bball

  I wrote a scraper using python a while back, and it worked fine in the command line. I have made a GUI for the application now, but I am having trouble with one issue. When I attempt to update text inside the gui (e.g. 'fetching URL 12/50'), I am unable seeing as the function within the scraper is grabbing 100+ links. Also when going from one scraping function, to a function that should update the gui, to another function, the gui update function seems to be skipped over while the next scrape function is run. An example would be: scrapeLinksA() #takes 20 seconds updateInfo("LinksA done") scrapeLinksB() #takes another 20 seconds in the above example, updateInfo is never executed, unless I end the program with a KeyboardInterrupt. I'm thinking my solution is threading, but I'm not sure. What can I do to fix this? I am using: PyQt4 urllib2 BeautifulSoup

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• Thread safety of Matlab engine API

  - by Jeremy

  I have discovered through trial and error that the MATLAB engine function is not completely thread safe. Does anyone know the rules? Discovered through trial and error: On Windows, the connection to MATLAB is via COM, so the COM Apartment threading rules apply. All calls must occur in the same thread, but multiple connections can occur in multiple threads as long as each connection is isolated. From the answers below, it seems that this is not the case on UNIX, where calls can be made from multiple threads as long as the calls are made serially.

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• Connecting to multiple firebird Databases via Delphi

  - by Branden

  I am integrating a system with 2 other applications, 1 using a Firebird database whilst the other BIS (using ADO). My delphi application uses Firebird. I need to read data from my database, insert it into both the BIS database and the other application firebird database. I have created seperate data modules for each. Sending data to the ADO works fine, but when writing to the other Firebird DB (my db still open) I get strange errors. I have managed to isolate the problem to the second firebird DB. Small data writes seems fine. The data structures are completly different, so un able to use a synch tool. is there a way to overcome this by using multi threading or seperate memory space each Firebird instance uses?

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• Multithreading in Lua

  - by RCIX

  I was having a discussion with my friend the other day. I was saying how that, in pure Lua, you couldn't build a preemptive multitasking system. He claims you can, because of the following reason: Both C and Lua have no inbuilt threading libraries [OP's note: well, Lua technically does, but AFAIK it's not useful for our purposes]. Windows, which is written in mostly C(++) has pre-emptive multitasking, which they built from scratch. Therefore, you should be able to do the same in Lua. The big problem i see with that is that the main way preemptive multitasking works (to my knowledge) is that it generates regular interrupts which the manager uses to get control and determine what code it should be working on next. I also don't think Lua has any facility that can do that. My question is: is it possible to write a pure-Lua library that allows people to have pre-emptive multitasking?

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• Allowing threads from python after calling a blocking i/o code in a python extension generated using

  - by SS

  I have written a python extension wrapping an existing C++ library live555 (wrapping RTSP client interface to be specific) in SWIG. The extension works when it is operated in a single thread, but as soon as I call the event loop function of the library, python interpreter never gets the control back. So if I create a scheduled task using threading.Timer right before calling the event loop, that task never gets executed once event loop starts. To fix this issue, I added Py_BEGIN_ALLOW_THREADS and Py_END_ALLOW_THREADS macros manually in the SWIG auto generated wrapper cxx file around every doEventLoop() function call. But now, I want to do the same (i.e. allow threads) when SWIG generates the code itself and not to change any code manually. Has anyone done something similar in SWIG? P.S. - I would also consider switching to any other framework (like SIP) to get this working. I selected SWIG over any other technology is because writing SWIG interface was really very easy and I just had to include the existing header files.

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• Multiple port asynchronous I/O over serialport in C#

  - by firoso

  I'm trying to write a test application for serial I/O (RS-232) with multiple units in C# and I'm running into an issue with my lack of threading experience so I'm soliciting feedback for a best known method. I've got a pool of COM ports COM1-16 each of which can read/write at any time and I need to be able to manage them simultaneously. Is this a situation for a thread pool? What is some guidance on structuring this applet? Edit: Upon review I was wondering is I really even need to do asynchronous threads here, I could just maintain states for each COM-port and do flow logic (i.e., statemachine) for each COM-port individually.

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• Async Socket Listener on separate thread - VB.net

  - by TheHockeyGeek

  I am trying to use the code from Microsoft for an Async Socket connection. It appears the listener runs in the main thread locking the GUI. I am new at both socket connections and multi-threading all at the same time. Having a hard time getting my mind wrapped around this all at once. The code used is at http://msdn.microsoft.com/en-us/library/fx6588te.aspx Using this example, how can I move the listener to its own thread? Public Shared Sub Main() ' Data buffer for incoming data. Dim bytes() As Byte = New [Byte](1023) {} ' Establish the local endpoint for the socket. Dim ipHostInfo As IPHostEntry = Dns.GetHostEntry(Dns.GetHostName()) Dim ipAddress As IPAddress = ipHostInfo.AddressList(1) Dim localEndPoint As New IPEndPoint(ipAddress, 11000) ' Create a TCP/IP socket. Dim listener As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp) ' Bind the socket to the local endpoint and listen for incoming connections. listener.Bind(localEndPoint) listener.Listen(100)

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• Looking for an explanation of the 'Asynchronous' word in .Net?

  - by IbrarMumtaz

  I need someone to explain the following names; Asynchronous Delegates. Asynchronous methods. Asynchronous events. I'm currently going over this for my 70-536 exam and I am covering all my bases so far. The threading chapter and online resources have been good to me on my second read through. Still though, the names used above mean absolutely nothing to me? I would really appreciate the meaning behind the word 'Asynchronous' and its relevance to Delegates, methods and events. Feel free to go into as much detail as you like. Thanks, Ibrar

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• Which thread invokes SensorEventListener.onSensorChanged

  - by Christoph Heindl

  From my records it seems that SensorEventListener.onSensorChanged callback is called by the same thread that registered the callback. I.e there must be some message-queue synchronization going on in the background which allows the activitys UI-Thread to handle the callbacks. That leads to my question: Is there a need to synchronize SensorEventListener.onSensorChanged with the activitys UI-thread, assuming that the activitys UI-thread registered the SensorEventListener? I cannot find any documentation references, but can see various examples calling invalidate() unsychronized or synchronize the entire callback. I used something along the lines of Log.i(TAG, "" + Thread.currentThread().getId()); to retrieve threading information. I'm running android 2.1 update1. Best regards, Christoph

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• How to stop ReSharper from showing error on a lambda expression where Action is expected?

  - by carlmon

  In Silverlight, System.Windows.Threading's Dispatcher.BeginInvoke() takes an Action<T> or a delegate to invoke. .NET allows me to pass just the lambda expression. but ReSharper sees it as an error, saying "Cannot resolve method 'BeginInvoke(lambda expression)'": Dispatcher.BeginInvoke(() => { DoSomething(); }) The error goes away if I explicitly create the Action around the expression like this: Dispatcher.BeginInvoke(new Action<object>(o => { DoSomething(); })); I prefer the least amount of code in this case for the best readability. Is there a way to disable this specific ReSharper error notification? I tried some of the options, but could not find it. Thanks, Carl

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